The present invention relates to a pig, in particular an inspection or cleaning pig, for traveling through an elongate pipe, preferably a gas pipeline, the pig having at least one functional unit for cleaning the pipe and/or for recording pipe information and also a plurality of magnets. Pipe information may be, for example, information on the position of cracks, points of corrosion, pipe (wall) deformations or diameters.
The prior art according to EP 1 828 764 B1 discloses a pig which has a functional unit for recording pipe information for the identification of defects in the pipe wall. For this purpose, the pig has a plurality of magnets, which magnetize the pipe wall in a region that can be scanned by the sensors. A disadvantage of the passively moved pigs is that, depending on the operating medium and the friction produced in the pipe, they may move along at different rates. For example, the friction increases at cross-sectional constrictions of the pipe, and so the speed of the pig is reduced. As a consequence, in particular in the case of a gas pipeline, pressure builds up behind the pig, and then strongly accelerates the pig at the moment that the frictional resistance is overcome. This leads to inferior quality of the data of the measurement, even to the extent of failure of the measurement for the region in which the pig is moved along above a critical speed of for example 5 m/s.